AU2014270689A1

AU2014270689A1 - Multistage self-suctioning centrifugal pump unit

Info

Publication number: AU2014270689A1
Application number: AU2014270689A
Authority: AU
Inventors: Aage Bruhn; Bjarne VINTHER TOFT
Original assignee: Grundfos Holdings AS
Current assignee: Grundfos Holdings AS
Priority date: 2013-05-22
Filing date: 2014-04-29
Publication date: 2015-12-03
Anticipated expiration: 2034-04-29
Also published as: RU2015149820A; RU2636288C2; CN105229309B; AU2014270689B2; US10337516B2; CN105229309A; WO2014187648A1; US20160084253A1

Abstract

The multistage self-suctioning centrifugal pump unit has at least two pump stages (4) which are arranged one after the other in the main direction of flow (32) and have a return flow channel (13) extending parallel to at least one pump stage (4). The return flow channel (13) opens in the main direction of flow (32) behind the first or an additional pump stage (4).

Description

1 Description The invention relates to a multi-stage, self-priming centrifugal pump assembly with the 5 features specified in claim 1. A multi-stage centrifugal pump assembly according to the preamble is known from EP 2 505 842 Al, which is designed such that a self-priming behaviour is achieved with only a small quantity of delivery fluid. The centrifugal pump assembly described there has proven its worth, 10 but requires a certain start-up time for the self-priming process. From DE 44 15 157 Al, it is counted as belonging to the state of the art, with a multi stage centrifugal pump, to lead back the delivery fluid during the suction phase by way of opening a non-return valve. Moreover, an air separator is provided, so that the air located in the 15 assembly, during the suction phase, can be replaced by fluid which is stored in a chamber of the pump, by which means a self-priming of the pump can be ensured. It is the object of the present invention, to further improve a centrifugal pump assembly of the type according to the preamble, with respect to its self-priming behaviour. 20 According to the invention, this object is achieved by a multi-stage, self-priming centrifugal pump assembly with the features specified in claim 1. Advantageous designs of the invention are specified in the dependent claims and the subsequent description as well as the drawing. Hereby, according to the invention, the features specified in the dependent claims and 25 description can form the solution according to the invention and according to claim 1, in each case on their own, but also in a suitable combination. The multi-stage, self-priming centrifugal pump assembly according to the invention comprises at least two pump stages which are consecutive in the flow direction, as well as a 30 backflow channel which lies parallel to at least one pump stage. According to the invention, the backflow channel is designed and arranged such that it runs out downstream of the first or a further pump stage, seen in the main flow direction of the pump, and specifically downstream of the diffuser (guide vane mechanism) of the pump stage, seen in the main flow direction. 35 The basic concept of the solution according to the invention is not to arrange the backflow channel parallel to the first pump stage, as is the case with the state of the art, but to arrange this in parallel to the second or one or more further pump stages. Thereby, with regard to the centrifugal pump assembly according to the invention, it is the case of one, with which the pump stages are arranged vertically above one another. Surprisingly, it has seen found that if, 2 according to the invention, the backflow channel is arranged downstream of the first or a further pump stage seen in the main flow direction of the pump, and specifically downstream of the diffuser of the pump stage, the procedure of the self-priming is effected in a significantly more intensive manner and in particular in a shorter temporal course, which is advantageous since the 5 time of the self-priming of the pump is shortened and thus the pump is available for its envisaged application , for example for delivering extinguishing fluid, at a much earlier stage. Although a certain basic quantity of fluid is required with the centrifugal pump assembly according to the invention, in order to initiate the self-priming procedure, the subsequent suctioning i.e. the generation of a vacuum is effected significantly more quickly than with pumps according to the 10 state of the art. Unnecessary eddying in the led-back fluid is prevented in the region of the diffuser due to the fact that the leading-back of the delivered fluid is not effected between the impeller and the diffuser, as is known from the state of the art, but downstream of the diffuser in the flow direction. The part of the fluid which is delivered through the pump stage/pump stages before the run-out of the return channel, is led through the diffuser without disturbing influences 15 of the led-back fluid, which is to say that the kinetic energy at the exit of the impeller can be converted into pressure energy by the subsequent diffuser and only then is a mixing with the led back fluid effected. A significant improvement of the self-priming procedure can be achieved on starting the pump by way of this. 20 It is advantageous if the backflow channel runs out downstream of the first pump stage seen in the main flow direction, thus downstream of the diffuser of the first pump stage, at the exit of this pump stage which is at the flow side. The backflow channel according to the invention can thereby bridge one or more pump stages and preferably this should bridge at least two pump stages. A particularly quick and good suction behaviour results if the suction channel 25 bridges four pump stages, thus for example is led parallel to the second to fifth pump stage. It is advantageous if the backflow channel seen in the main flow direction runs out downstream of the first pump stage, thus downstream of the diffuser of the first pump stage, at the exit of this pump stage which is at the flow side. 30 It is advantageous to provide a gas separator within the centrifugal pump assembly, said gas separator according to a further development of the invention preferably being arranged at the exit side of the at least second pump stage, in order to design the suction procedure as effectively as possible. With regard to the main flow direction, it is useful to arrange the gas separator downstream of the pump stages provided for the suction procedure, thus subsequently 35 to the pump stages to which the backflow channel lies in parallel. According to one advantageous design of the invention, the gas separator is formed by a housing-fixed, tubular body which connects onto a diffuser of a pump stage and which in its wall comprises at least one recess connected to the backflow channel in a fluid-leading manner. Such 3 an arrangement is inexpensively manufacturable and highly effective, since the conveying fluid gas mixture exiting the diffuser with swirling rises helically on the tubular body and due to the centrifugal force gets through the at least one recess in the wall and thus into the backflow channel, whereas the gas is led upwards and is thus removed from the suction circulation. 5 According to an advantageous further development of the invention, a buffer chamber is arranged between two pump stages which are subsequent to the first pump stage in the main flow direction. Such a buffer chamber is preferably arranged downstream of the gas separator in the main flow direction. The buffer chamber serves for storing a certain quantity of water within the 10 pump and in particular when suctioning larger air bubbles, as can occur for example on suctioning an emptying tank towards the end, ensures that these air bubbles do not lead to water necessary for the suctioning procedure being delivered out of the pump. The buffer chamber is therefore to be designed such that on the one hand it is automatically filled given flow through the pump, but one the other hand that it releases the delivery fluid stored there, at least in a 15 delayed manner, i.e. leads it via the backflow channel back again into the pump stages provided for the suctioning procedure. According to the invention, such a buffer chamber can advantageously be formed by a housing-fixed, tubular body which surrounds the common drive of the centrifugal pump 20 assembly at a distance and which is arranged at a distance to the outer housing wall. This tubular body is connected via an annular base which on the one hand is connected to the tubular body and on the other hand to the wall of the pump and comprises at least one recess connected to the backflow channel in a fluid-leading manner. It is therefore the case of an annular storage reservoir between the tubular body and the pump wall, in which recesses are provided on the 25 base side and these recesses are designed such that the backflow through these recesses with regard to time runs such that an entrained large gas bubble does not lead to the self-priming behaviour being compromised. According to a further development of the invention, one envisages the backflow channel 30 being able to be shut off via a valve controlled in a pressure-dependent manner, on the one hand to ensure a good suctioning behaviour and on the other hand however to ensure that no efficiency reduction of the pump is effected by the backflow channel in normal operation. Preferably, such a valve is provided at the entry side of the backflow channel, since a comparatively high pressure of the fluid delivery already prevails there at the exit of a second pump stage or one lying 35 thereabove, and this high pressure can be used for the control of the valve, in particular for its shut-off. The valve is advantageously controlled by differential pressure, and specifically in dependence on the differential pressure at the backflow channel, so that the backflow channel is shut off on exceeding a predefined differential pressure. In this manner, it is ensured that the 4 backflow channel is only effective for the actual suctioning procedure and has no efficiency worsening influence in normal operation of the pump. Preferably, the backflow channel is designed as an annular channel which surrounds at 5 least, one preferably however two to four pump stages. According to a further development of the invention, means for preventing the pump from running empty are provided. These are to be selected depending on the application of the pump. Thus according to the invention, if the assembly is envisaged and designed exclusively for 10 operation with pump stages arranged vertically above one another and comprises a suction connection at the foot of the pump, a pipe section can be arranged upstream of this suction connection, and this pipe section extends laterally of the assembly, preferably up to the height of the last pump stage. By way of this pipe section, it is ensured that the centrifugal pump assembly cannot run empty due to the backflow of delivery fluid. Thus the self-priming behaviour also 15 largely ensured in this manner. Thereby, basically the pipe section arranged upstream is to be led up so high, that at least one of the pump stages lying in the region of the backflow channel and are thus are required for the self-priming behaviour, is reached. According to an advantageous further development of invention, the pipe section 20 arranged upstream is designed in a U-shaped manner and at its region connecting the limbs of the U, thus at its upper end, is provided with a ventilation opening which can be selectively opened and closed by way of a ventilation valve. The ventilation opening in particular with a suction conduit leading further downwards, ensures that the pipe section arranged upstream and thus also the pump connecting thereto are prevented from being suctioned dry due to the vacuum in the 25 suction conduit. Then the part of the suctioning conduit leading the vacuum can be filled with air by way of opening the valve, thus by way of releasing the ventilation opening, so that the other limb of the pipe section and thus also the pump itself remain filled with fluid, with a later starting operation of the pump, and the pump starts up again in a self-priming manner. Advantageously thereby, the ventilation opening is conductively connected to the pressure space of the last pump 30 stage amid the intermediate connection of the ventilation valve, so that given an opened ventilation valve, it is always ensured that the pipe section close to the pump, as well as the pump itself remain filled with fluid, irrespective of the pressure conditions in the other pipe section, thus at the suctioning conduit. 35 Advantageously, an electrically controllable solenoid valve is applied as a ventilation valve. Such valves are inexpensive, reliable and simple to activate. Alternatively, a non-return valve can also be arranged on the suction side, i.e. upstream of the first pump stage, for preventing the pump from running empty. Such a non-return valve can 5 be part of the pump assembly or also be arranged in a pipe section arranged upstream on the suction side. Advantageously, a delivery connection is arranged in the foot of the pump and is 5 conductively connected via an annular space to the last pump stage. A pump of the inline construction manner is formed by way of this. According to the invention, advantageously an electric motor which drives a central shaft carrying the impellers is provided for the drive of the centrifugal pump assembly. The motor is 10 advantageously arranged on the upper side of the assembly. The invention is hereinafter explained by way of embodiment examples represented in the drawing. There are shown in: 15 Fig. 1 in a greatly simplified schematic representation, a longitudinal section through a centrifugal pump assembly according to the invention, Fig. 2 in an enlarged representation, the region of the first four pump stages of Fig. 1, 20 Fig. 3 in an enlarged representation, the region between the fourth and the last pump stage in Fig. 1, Fig. 4 in an enlarged representation, the pressure-side housing region behind the fourth pump stage, in a longitudinal section, 25 Fig. 5 the housing region according to Fig. 4, in cross section, Fig. 6 the centrifugal pump assembly according to Fig. 1, with an incorporated valve and 30 Fig. 7 one embodiment variant with a non-return valve connected upstream, according to Fig. 1. With regard to the centrifugal pump assembly represented by way of the Figures I to 5, it 35 is the case of a multistage, self-priming centrifugal pump assembly of the inline construction type which is envisaged for vertical operation, thus standing upright. Thereby, only the pump side part of the centrifugal pump assembly which is provided on a foot part 1 for standing placement on a horizontally aligned surface and which comprises a suction connection 2 as well as a delivery connection 3 aligned thereto, as is common with inline pumps, is represented in 6 Fig. 1. A middle pump part 5 connects to this foot part 1 formed as a cast metal component and this middle pump part comprises the pump stages 4 and at its upper end is closed off by a head part 6 likewise formed from cast metal and simultaneously forming a motor base 7 for the electric motor to be connected there. This (not shown) electric motor is connected via a (likewise 5 not represented) coupling to a central shaft 8 which passes through the pump from the head part 6 to the foot part 1, is rotatably mounted and carries impellers 9 of the pump stages 4. The pump represented by way of Figures I to 5 as a whole comprises five pump stages 4 which are connected hydraulically in series so that the delivery fluid is led from the suction 10 connection 2 firstly to the lowermost, first impeller 9a, from there into the diffuser 10a assigned to this impeller 9a and leading the delivery fluid to the pump stage arranged downstream, specifically to the suction port of the impeller 9b of the second pump stage to which second pump stage a diffuser l0b leading the fluid to the suction port of an impeller 9c of the third pump stage is assigned. The fourth pump stage consisting of the impeller 9d and the diffuser 10d 15 connects to the third pump stage which is closed off by the diffuser 10c. Finally, the pump close to its upper end comprises a fifth pump stage consisting of an impeller 9e and a diffuser 1 Oe. The pump stages 4 are arranged in a cylindrical inner casing 11 which is surrounded at a radial distance by a likewise cylindrical outer casing 12. The delivery fluid is led via the annular 20 space formed between the inner casing 11 and the outer casing 12, from the exit of the diffuser 10e of the uppermost, fifth pump stage back downwards to the lower foot part 1 and there to the delivery connection 3. The basic construction of the pump as well as the pump stages in each case consisting of 25 an impeller 9 and a diffuser 10 corresponds to that which is common, is counted as belonging to the state of the art and is therefore not described in detail here. In order to design the pump in a self-priming manner, i.e. to ensure with regard to design that a self-priming effect happens at least when a small quantity of fluid is located within the 30 pump, several design measures are envisaged with the represented centrifugal pump. Thus a backflow channel 13 is provided, which is formed by a cylindrical intermediate wall arranged at a small distance to the inner casing 11 between the exit of the first pump stage and the exit of the fourth pump stage and is otherwise connected at the ends to the inner casing 35 11 in a fixed and sealed manner. The backflow channel 13 arises due to radial recesses 14 above the fourth pump stage, thus above the diffuser 10d of the fourth pump stage in the inner casing 11. The backflow channel 13 runs as an annular channel downwards from the recesses 14, where it runs out through recesses 15 between the diffuser 10a at the exit side of the first stage and the impeller 9b at the entry side of the second pump stage. This backflow channel 13 thus short 7 circuits the fourth pump stage with the exit of the first pump stage, so that the delivery fluid during a suctioning phase of the pump after switching on firstly circulates between the second and the fourth pump stage, as is indicated by the interrupted lines 16 in Fig. 2, said lines representing the suctioning fluid circulation. The self-priming is effected in a comparatively 5 rapid manner due to the fact that the backflow channel 13 is not led back to the entry of the first pump stage as is the case with the state of the art, but to the entry of the second pump stage. A gas separator 17 in the form of a cylindrical pipe section is formed at the exit side of the fourth pump stage within the inner casing 11, in a manner connecting to the diffuser 1 Od of 10 this stage, and this pipe section is arranged in a manner fixed to the housing and coaxially to the shaft 8 and in the region of the upper third of its length is provided with circular recesses 18. The pipe forming the gas separator 17 with regard to height corresponds roughly to two pump stages. The gas separator 17 has the effect that on interruption of the flow of the fluid due to a relatively large gas bubble, this can rise centrally, whereas the fluid which exits from the diffuser 10d, due 15 to the swirling which is still present and the centrifugal force resulting from this, exits through the openings 18 to the outside and then flows back at the outer periphery within the inner casing 11 or rises further upwards, without the delivery flow breaking away due to this. A buffer chamber 19 which is delimited inwards coaxially to the shaft 8 by a cylindrical 20 pipe section 20, is delimited to the outside by the inner casing 11 and is delimited to the bottom by an annular base 21, connects onto the gas separator 17 to the top at a distance. The base 21 is provided with recesses 22 which are dimensioned such that the buffer chamber 19 due to the recesses 22 in the base 21 empties only very slowly but not spontaneously, thus that delivery fluid firstly remains in this region of the pump even in the case of a passage of larger gas 25 quantities. The suction port of the impeller 9e of the fifth pump stage connects to the top onto the cylindrical pipe section 20 at a distance. The delivery fluid which gets through the pipe section 20 thus at least partly flows into the buffer chamber 19 arranged laterally next to it and from there, as long as these spaces are not filled with delivery fluid as in normal pump operation, back to the fourth pump stage and from there via the backflow channel 13 to the entry of the second 30 pump stage. In this manner, even with the occurrence of larger gas bubbles, it is always ensured that sufficient delivery fluid remains within the pump, in order to ensure the continuous delivery operation. A pressure-controlled valve 23 is provided which, when the pressure at the exit of the 35 fourth pump stage rises above a certain value, specifically when the actual suctioning procedure is completed, closes the recesses 14 in the inner casing 11, in order to prevent losses arising after the suctioning phase in the actual delivery operation due to delivery fluid flowing back though the backflow channel 13. For this, the valve 23 comprises a sheet-metal strip 24 which is arranged within the cylindrical outer inner contour in a limitedly movable manner, at its two ends 8 is designed in a fork-like manner and is connected to the inner casing 11 in a limitedly movable manner within this by way of screws 25. The sheet-metal strip 24 in the region of the screws 26 is held in a manner distanced to the inner casing 11 via a screw 26 in the inner casing 11, said screw being arranged centrally between the screws 25 and between the two recesses 14. The 5 sheet-metal strip 24 which is formed from spring steel is elastically deformed with an increasing inner pressure and is pressed radially outwards in a manner closing the recesses 14. As soon as the inner pressure drops below a certain value, the sheet-metal strip 24 again assumes its original shape represented in Fig. 5 and thus opens the recesses 14. 10 A U-shaped pipe section 27 is arranged upstream of the suction connection 2 in order to prevent the centrifugal pump from running empty after switching off for example, and this pipe section with regard to height extends up to the fifth pump stage, so that the pump itself and the limb of the U-shaped pipe section 27 which is on the left in Fig. 1 always remains filled with delivery fluid. 15 Thereby, in a further development, the U-shaped pipe section 27 at its uppermost location, thus in the web region of the U can comprise a bleed connection 28 which is closed by way of a solenoid valve 29. This bleed connection 28 is connected to the pressure space of the last pump stage via a flexible tube 30. The solenoid valve 29 is closed in the non-actuated 20 condition and is opened by way of a suitable (not shown) control, given a pressure drop in the pressure space of the last pump stage, in order to ensure that sufficient delivery fluid always remains within the pump and the self-priming capability is retained. With the embodiment according to Fig. 7, a non-return valve 31 is provided on the 25 suction side instead of the U-shaped pipe section 27 and the bleed opening 28, and this valve endures that delivery fluid can only flow into the pump but not out of this at the suction side, and the self-priming capability is also ensured by way of this.

9 List of reference numerals 1 foot part 5 2 suction connection 3 delivery connection 4 pump stages 5 middle pump part 6 head part 10 7 motor base 8 shaft 9a-9e impellers lOa-l0e diffusers 11 inner casing 15 12 outer casing 13 backflow channel 14 recesses top 15 recesses bottom 16 interrupted lines which represent the delivery flow in the suction phase 20 17 gas separator 18 recesses 19 buffer chamber 20 pipe section 21 base of buffer chamber 25 22 recesses in base 23 valve 24 sheet-metal strip 25 screws 26 screw 30 27 U-shaped pipe section 28 bleed connection 29 solenoid valve 30 flexible tubing 31 non-return valve 35 32 delivery flow in normal pump operation, main flow direction

Claims

1. A multi-stage, self-priming centrifugal pump assembly with at least two pump stages (4) which are consecutive in the main flow direction (32) and with a backflow channel (13) which lies parallel to at least one a pump stage (4) and which runs out downstream of the first or a further pump stage (4) in the main flow direction (32), characterised in that the backflow channel (13) runs out downstream of the diffuser (1Oa) of the pump stage (4).

2. A centrifugal pump assembly according to claim 1, characterised in that the backflow channel (13) runs out downstream of the diffuser (10a) of the first pump stage (4), in the main flow direction (32).

3. A centrifugal pump assembly according to claim 1 or 2, characterised in that a gas separator (17) is arranged at the exit side of the at least second pump stage (4).

4. A centrifugal pump assembly according to claim 3, characterised in that the gas separator (17) is formed by a housing-fixed, tubular body (17) which connects onto a diffuser (10) of a pump stage (4) and which in its wall comprises at least one recess (18) connected to the backflow channel (13) in a fluid-leading manner.

5. A centrifugal pump assembly according to one of the preceding claims, characterised in that a buffer chamber (19) is arranged between two pump stages (4) which follow the first pump stage (4) in the main flow direction (32), and preferably downstream of the gas separator (17) in the main flow direction (32).

6. A centrifugal pump assembly according to claim 5, characterised in that the buffer chamber (19) is formed by a housing-fixed, tubular body (20), a housing wall (11) surrounding this at a distance and an annular base (21) connecting these, said base comprising at least one recess (22) which is connected to the backflow channel (13) in a fluid-leading manner.

7. A centrifugal pump assembly according to one of the preceding claims, characterised in that a valve (23) is provided preferably on the entry side of the backflow channel (13) and is controlled in a pressure-dependent manner and shuts off the backflow channel (13) on exceeding a predefined differential pressure.

8. A centrifugal pump assembly according to one of the preceding claims, characterised in that the backflow channel (13) is an annular channel surrounding at least one pump stage (4). 11

9. A centrifugal pump assembly according to one of the preceding claims, characterised in that means for preventing an empty running of the pump are provided.

10. A centrifugal pump assembly according to one of the preceding claims, characterised in that the assembly is designed for operation with pump stages (4) arranged vertically above one another and comprises a suction connection (2) at the foot (1) of the pump, wherein a pipe section (27) which extends laterally of the assembly, preferably up to the height of the last pump stage (4), is arranged upstream of the suction connection (2).

11. A centrifugal pump assembly according to claim 10, characterised in that the pipe section (27) arranged upstream is designed in a U-shaped manner and at its region connecting the limbs of the U is provided with a ventilation opening (28) which can be selectively opened or closed by way of a ventilation valve (29).

12. A centrifugal pump assembly according to claim 11, characterised in that the ventilation opening (28) is conductively connected to the pressure space of the last pump stage (4), amid the intermediate connection of the ventilation valve (29).

13. A centrifugal pump assembly according to one of the preceding claims, characterised in that the ventilation valve (28) is an electrically controllable solenoid valve.

14. A centrifugal pump assembly according to one of the preceding claims, characterised in that a non-return valve (31) is arranged upstream of the first pump stage (4).

15. A centrifugal pump assembly according to one of the preceding claims, characterised in that a delivery connection (3) which is conductively connected to the last pump stage (4) via an annular space, is arranged in the foot (1) of the pump.

16. A centrifugal pump assembly according to one of the preceding claims, characterised in that an electric motor is provided for the drive of a central shaft (8) carrying the impellers (9a e) and is arranged at the upper end of the assembly.